Ubiquitin C-terminal hydrolase L1 (UCHL1) is a multifunctional brain protein that has been implicated in Parkinson's and Alzheimer's Diseases. Reactive lipid species including cyclopentenone prostaglandins (CyPgs) are produced in ischemic brain and covalently adduct the 152 cysteine (C152) of UCHL1, significantly alter the 3D structure of the enzyme, inhibit hydrolase activity and induce aggregation of the protein. UCHL1 hydrolase activity protects neurons against hypoxic injury in vitro. In new preliminary data, we have found that a cysteine 152 to alanine mutation in UCHL1 (UCHL1 C152A) is resistant to binding to CyPgs and protects neurons from CyPg toxicity, anoxia and oxygen-glucose deprivation (OGD). Neurites of primary neurons are very sensitive to CyPg injury, and the UCHL1 C152A-derived neurites are resistant to CyPg induced fragmentation compared to wild type neurites. Mutant UCHL1 C152A mice have smaller infarctions and improved short term motor outcome after middle cerebral artery occlusion (MCAO) compared to wild type mice. Based on these data, we hypothesize that CyPgs and other reactive lipid species bind to C152 of UCHL1 and inactivate the enzyme, exacerbate injury, and limit recovery of function after ischemic injury. The following aims will be addressed: 1. Test the hypothesis that the UCHL1 C152A mutation protects primary cultured neurons from hypoxia/ischemia and CyPgs in vitro. 2. Determine how the UCHL1 C152A mutation alters the function of the UPP, autophagy, ER stress, and ubiquitination of target proteins after OGD, hypoxia and CyPg treatment in primary neurons. 3. Test the hypothesis that the UCHL1 C152A mutation increases survival of both gray and white matter and improves behavioral outcome after middle cerebral artery occlusion in mice. Methodology: In vitro methods include cell viability/cell death assays, neurite and axon outgrowth quantification, Western blotting, protein ubiquitination, proteomic analysis; in vivo methods include MCAO in mice, long term behavioral outcome, quantification of gray, white matter, myelin, axons and synapses, Western blotting,UCHL1 activity measurement and comparison of electrophysiological function. The proposed studies will address a novel mechanism by which the brain recovers from cerebral ischemia and may suggest new therapeutic strategies that may improve long term motor and cognitive function after stroke.